This invention relates to a method of controlling the ignition of an internal combustion engine and more particularly to an improved engine ignition control system.
It is well known to equip internal combustion engines with some form of protective device which will, in response to a predetermined engine abnormal condition, reduce the speed of the engine so as to prevent damage. Such devices may reduce the speed of the engine in response to a number of conditions such as overheating, lack of adequate lubrication pressure, or lack of adequate cooling liquid flow through the engine cooling jacket. All of these arrangements employ one or more sensing devices for sensing at least one of the noted abnormal engine conditions and for giving an alarm when such abnormal condition occurs. When there is such an abnormality noted, the speed of the engine is reduced so as to protect the engine. The speed reduction may be accomplished either by interrupting the firing of the spark plugs or by force misfiring of the spark plugs or a combination of the two.
When the engine is slowed in this manner, there is the possibility that burning may either continue or become initiated in the exhaust system. Such conditions are known as backfiring or firing back and result from the admission of a combustible mixture into the exhaust system. In order to provide such backfiring or firing back in the exhaust system, many of these devices also employ an arrangement for retarding the spark when the engine speed is being reduced in the aforenoted manner, which spark retardation has the effect of precluding the likelihood of backfiring in the exhaust system.
Although such combined spark interruption and/or misfiring with spark retardation is effective in protecting the engine and also precluding firing back, it can have the effect of increasing the temperature in the exhaust system. There are many instances when such temperature elevation in the exhaust system is undesirable. For example, in marine applications, it is the normal practice to cool the exhaust gases by adding cooling water to them when they are discharged from the engine. Because of the fact that the exhaust gases are normally cooled, it is possible to use rubber or elastomeric expansion joints in the exhaust system. However, if the exhaust temperature becomes too high due to the reduction of the engine speed by misfiring or interrupted firing and retardation of the spark, these elastic joints can be damaged.
It is, therefore, a principal object of this invention to provide an improved method and apparatus for controlling the ignition of an internal combustion engine so as to slow the speed of the engine in the event an abnormal condition is sensed, to insure against backfiring in the exhaust system and also so as to insure that the exhaust system does not become overheated under such slowing conditions.
It is a further object of this invention to provide an improved method and apparatus for controlling the spark advance during engine slowing because of an abnormal condition in such a manner that backfiring and excess exhaust gas temperatures are avoided.